1. Field of the Invention
The present invention is generally applicable to the ultrasonic inspection of conduits. More particularly, the inspection method and apparatus of the present invention permit differentiation between defects in conduits and deposits of foreign materials associated with conduits.
2. The Prior Art
Ultrasonic inspection probes useful in the inspection of conduits are known. Such probes generally contain multiple (typically eight) individual transceiver elements all pointing toward the conduit at the same general angle and equally spaced around the probe body, each of which inspects a particular section of the conduit. These probes are capable of detecting both simulated cracks and actual cracks produced in laboratory samples of tubing. An example of such a probe is the Aerotech boreside array transducer.
However, during the first extensive field use of such ultrasonic inspection probes, a large number of defect-like sounds were detected which could not be verified upon visual inspection of the conduit. It was subsequently determined that non-detrimental deposits of materials on the exterior of the conduits were producing these sounds.
The Nondestructive Testing Handbook, Vol. II, pp. 49.8-49.13, The Ronald Press Company, New York (1959) discloses a search unit employing separate transmit-receive search units in a so-called, "pitch-catch" relationship. However, this arrangement would not provide sufficient information to distinguish defects from deposits of materials on the exterior of the conduit since the sound is only directed from one direction.
The ultrasonic sound reflected by a defect and the sound reflected by a deposit produce electronic signal responses which appear very similar. Thus, in many instances, a deposit is indistinguishable from a defect. Accordingly, there is a need for improvement in the means and methods employed for inspecting such conduits in order to avoid unnecessary repair or replacement of conduits which contain no defects.